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Tumor Biology |
Departments of Cell Biology [L. U., C. D.], Pathology [M. K. R.], and Surgery (Neurosurgery), Neurology, and Cell Biology [E. C. H.], Memorial Sloan-Kettering Cancer Center, New York, New York 10021, and Department of Gynecologic Oncology - 440 [J. C. C.] and Pathology [G. N. F.], M. D. Anderson Cancer Center, Houston, Texas 77030
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ABSTRACT |
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 Top ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Signaling via Ras and Akt are both elicited from activated RTKs. Molecules such as Sos, Grb2, and Shc can mediate activation of Ras from a GDP-bound to a GTP-bound state. Ras-GTP can in turn activate downstream proteins such as Raf1 and Rac/Cdc42. Activation of these pathways control transcription, translation, apoptosis, and cytoskeletal rearrangements depending on cell type and cellular context (6)
. Ras/Erk activation has also been shown to regulate expression of proteins involved in G1 cell cycle control such as induction of cyclin D1 and decrease in p27KIP1 (7)
. Activation of Akt on the other hand is achieved by RTK activation of PI3k. This activation leads to the generation of the second messenger PtdIns(3
,4
,5)
P3, which in turn can activate PDK1/2 and Akt. The activation of PI3k is counteracted by the 3'phosphoinositol phosphatase PTEN (8, 9, 10, 11)
generating PtdIns(3
,4)
P2. Akt regulates many biological processes (also see "Discussion") by phosphorylation of its downstream targets, including the mammalian target of rapamycin, caspase 9, forkhead transcription factor, I
B kinase, glycogensynthasekinase-3ß, MDM2, and p21CIP1/p27KIP1 (12
, 13)
. In addition, there is cross-regulation between the Ras/Raf/Erk and PI3k/Akt pathways. Ras has been shown to activate PI3k (14)
, and Raf1 has been found to inhibit Akt (15
, 16)
. However, most of the pathways described have been elucidated from studies in fibroblasts and remain to be validated in astrocytes.
The INK4a-ARF tumor suppressor locus encodes two proteins, p16INK4a and p14ARF, which modulate the activity of the RB and p53 proteins (17)
. Deletion of this locus is one of the most frequent mutations found in human GBMs with a rate of 
60% (18)
. In those GBMs that retain an intact INK4a-ARF locus, mutations in other components of the p53 and RB pathways seem to be obligatory (2
, 3
, 19
, 20) . However, the role of INK4a-ARF loss in human gliomagenesis is not known. The result from reconstituting p16INK4a function in vitro in a human glioma cell line with homozygous deletion of the INK4a-ARF locus suggests that one role of INK4a-ARF deficiency may be to render cells immortal by disrupting their ability to enter G1 growth arrest and senescence (21)
. This hypothesis was further substantiated by a study showing that cultured primary mouse astrocytes deficient for the Ink4a-Arf locus are immortal and acquire characteristics of undifferentiated glia, including progenitor-like morphology, expression of nestin, and loss of Gfap expression (22)
.
The role of Ink4a-Arf in tumor suppression in mice has been extensively studied. Mice deficient for the Ink4a-Arf locus developed a variety of spontaneous tumors within their first year of life (23) . This phenotype could to a large extent be attributed to the loss of Arf alone as the Arf null mice showed most of the same traits as the Ink4a-Arf null mice (24) . In addition, Arf null mice developed a low frequency of spontaneous gliomas that has not been found in Ink4a-Arf null mice. The two different strains of Ink4a null mice that were recently generated showed a much lower tendency to spontaneous tumor formation than Ink4a-Arf or Arf null mice (25 , 26) . However, a few of these mice did develop spontaneous melanomas (26) , a tumor type not found in the Ink4a-Arf or Arf null mice. Moreover, when crossing Ink4a null mice with Ink4a-Arf null mice, the resulting Ink4a null Arf+/- mice showed a high susceptibility to develop carcinogen-induced melanomas while retaining the wt Arf allele (25) . Taken together, this implicates that there may be a complex and rather subtle interplay between the Ink4a and Arf loci depending on cellular context.
Our previous studies on mouse gliomagenesis using the RCAS/tv-a model system have shown that Ink4a-Arf loss is necessary to induce glioma-like lesions from both neural progenitors and astrocytes in cooperation with an activated epidermal growth factor receptor (27) . However, in platelet-derived growth factor B-induced oligodendrogliomas, experimental Ink4a-Arf loss is not required but accelerates tumor formation and enhances tumor progression (28) . This implies that the Ink4a-Arf locus may have diverse roles in gliomagenesis, either sensitizing cells to transformation or enhancing tumor progression, depending on cell type and oncogenic stimuli.
The RCAS/tv-a system allows postnatal gene transfer to specified cell types in the CNS of tv-a transgenic mice (29) . Oncogenes are delivered using RCAS (replication competent ALV splice acceptor) viral vectors, and only cells expressing tv-a, the receptor for ALV-A, can be infected and combinations of genes can be efficiently transduced either to primary cells in culture or in vivo. We have generated two different transgenic tv-a mouse lines, Ntv-a, expressing tv-a from the nestin promoter (27) , and Gtv-a, expressing tv-a from the GFAP promoter (30) . The nestin protein is expressed in neural progenitors of the CNS (31) , and GFAP is expressed in differentiated astrocytes (32) . During development of the CNS, the expression of these genes do not seem to overlap (33) .
Using the RCAS/tv-a system, we have demonstrated that combined gene transfer of activated forms of Akt and KRas into nestin-expressing neural progenitor cells (Ntv-a mice) resulted in the formation of tumors with the histological characteristics of human GBM (5) . The individual genes had no effect in Ntv-a mice, and the combination of KRas and Akt was equally ineffective in Gfap-expressing astrocytes (Gtv-a mice). Therefore, it appears that both the differentiation status of the cell-of-origin and the correct combination of oncogenes are essential for efficient glioma formation.
In this report, we have investigated the effect of experimental loss of the Ink4a-Arf locus on the formation of gliomas induced by KRas and Akt. We found that deletion of Ink4a-Arf allows GBM formation also from astrocytes and that it enhances gliomagenesis from neural progenitors. These gliomas have variable astrocytic character and, depending on the signal transduction pathways activated, closely resemble some of the variants of GBM seen in humans. The fact that all tumors induced in Gtv-a mice expressed nestin implies that one function of Ink4a-Arf loss in these tumors is to make differentiated astrocytes susceptible to oncogenic stimuli by promoting an undifferentiated phenotype of the cells.
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MATERIALS AND METHODS |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Mice.
Generation of the Ntv-a and Gtv-a wt and Ink4a-Arf-/- mouse lines has been described previously (27
, 30)
. The resulting genetic backgrounds of the transgenic mice used were a mixture of FVB/N, C57BL6, BALB/C, and 129.
Infection of Transgenic Mice.
DF-1 is an immortalized chicken cell line (American Type Culture Collection) that was used to produce RCAS-derived retroviruses as described previously (27)
. Infection of tv-a transgenic mice was performed as described in Ref. 27
. Mice were sacrificed when seriously ill or at 12 weeks of age. Statistical analysis was performed with the GraphPad software Prism3 using the log rank test applied to Kaplan-Meier graphs.
Brain Sectioning, H&E, and Immunostaining.
These procedures were performed as described previously (28)
. Antibodies used were monoclonal anti-GFAP (MAB3402; Chemicon), rabbit polyclonal anti-HA (Y-11; Santa Cruz Biotechnology), monoclonal antirat nestin (PharMingen), and immunohistochemistry-specific rabbit polyclonal antiphospho-Akt (Ser473; Cell Signaling Technology).
Infection of Primary Brain Cell Cultures and Growth Rate Analysis.
The establishment of primary astrocytes were done as described previously (28)
. The supernatants containing RCAS virons produced in DF-1 cells were collected and filtered through 0.22-µm filters followed by transferring into 70–80% confluent primary brain cell cultures. This was repeated three times with 12-h intervals. After infection, the proliferation rates were measured. Briefly, the cells were harvested by trypsin digestion and counted using a hemocytometer. After counting, 105 cells were replated and grown in DMEM with 10% FCS until the cells reached confluence. This procedure was repeated over time and duplicate samples were used. Finally, the total accumulated cell numbers were calculated and plotted as growth curves. Error bars show SDs.
Western Blot Analysis.
Whole cell lysates were prepared by dissolving 106 cells in 400-µl whole cell lysis buffer [100 mM NaCl, 30 mM Tris (pH 7.6), 1% NP40, 30 mM NaF, 1 mM EDTA, 1 mM sodium validate, 0.5 mM phenylmethylsulfonyl fluoride, and protease inhibitor mixture; Boehringer Mannheim], followed by lysis on ice for 45 min and pelleting of debris by centrifugation. Protein samples (40 µg) were separated by 10% SDS-PAGE and transferred to nitrocellulose. Filters were blocked for 1 h at room temperature in 5% dry milk in 1x TBS-T [Tris-buffered saline (pH 7.5) with 0.1% Tween 20]. The anti-HA primary antibody (Y-11; Santa Cruz Biotechnology) was used at 1:500 dilution in 5% BSA in 1x TBS-T and incubated at 4°C overnight. Secondary peroxidase-conjugated antirabbit antibody (Boehringer Mannheim) was used at 1:2000 dilution. Signals were visualized with enhanced chemiluminescence (Amersham) on Kodak X-OMAT films.
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RESULTS |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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.
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. To determine whether loss of Ink4a-Arf would contribute to gliomagenesis from astrocytes, we infected 31 Gtv-a Ink4a-Arf-/- mice with the combination of RCAS-KRas and RCAS-Akt and analyzed them for the formation of intracranial tumors. As shown in Fig. 1A
, 13 (42%) of the mice developed gliomas by the age of 12 weeks (P < 0.0001 compared with Gtv-a wt; KRas + Akt). These tumors were characterized by a mixture of small elongated cells and large pleomorphic cells, pseudopalisading with necrosis (Fig. 2A)
and hypervascularity. Tumors were nestin positive (Fig. 2B)
and had areas of strong Gfap expression (Fig. 2C)
. HA immunoreactivity was found in the majority of the tumors with varied intensity and extent (Fig. 2D)
. On the basis of histological and immunohistochemical data, these tumors represent, by virtue of Gfap expression in both the spindled and astrocytic cells, a morphological variant of GBM referred to as spindle cell GBM (34)
. In addition, a few of the tumors had rather extensive areas of giant, multinucleated cells (Fig. 2E)
that were nestin (Fig. 2F)
and HA (Fig. 2H)
positive for the most part, and some of the cells also expressed Gfap (Fig. 2G)
. These tumors are similar to another well-recognized subtype of GBM referred to as giant cell GBM.
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). In the Ntv-a Ink4a-Arf-/- mice, the incidence was found to be 21 of 43 (49%, P = 0.0049 compared with Ntv-a wt; KRas + Akt; Fig. 1B
). Therefore, Ink4a-Arf loss clearly contributes to tumor initiation from both differentiated and undifferentiated glia in this model system.
Histological analysis of the tumors induced in Ntv-a wt mice showed, in agreement with our previously described data (5)
, the typical characteristics of GBM, including necrosis with pseudopalisading, cellular pleomorphism, and positive immunostaining for Gfap and nestin (data not shown). By contrast, the histology of the tumors induced in Ntv-a Ink4a-Arf-/- mice (Fig. 3)
had a substantial spindled component similar to the spindled GBM tumors induced in Gtv-a Ink4a-Arf-/- mice. All regions of tumor-expressed nestin (data not shown) but Gfap expression were mainly confined to the gliomatous component of the tumor (Fig. 3B)
. These tumors, having a mixture of Gfap-negative spindled cells and Gfap-expressing astrocytic regions, resemble human GS, which are also composed of both sarcoma and GBM histologies.
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) and 10 of 30 in Gtv-a mice (33%, P = 0.0001 compared with Gtv-a wt; KRas + Akt; Fig. 1A
).
The KRas-induced tumors had, regardless of tv-a strain, the morphological appearance of primary brain sarcoma or the sarcomatous portion of GS. They consisted of tightly packed elongated cells that showed strong immunostaining for nestin and S100 (indicating glial lineage) and were, but for a few exceptions, negative for Gfap expression (data not shown). A few of the tumors induced in Gtv-a Ink4a-Arf-/- mice did, however, display histological features suggestive of glial differentiation. One resembled a GBM (Fig. 4A)
and expressed both nestin (Fig. 4B)
and Gfap (Fig. 4C)
, and another had extensive areas of giant cells (data not shown), similar to a giant cell GBM.
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Akt Activity Influences Tumor Cells toward an Astrocytic Phenotype.
Our results show that in both Ntv-a Ink4a-Arf-/- mice and Gtv-a Ink4a-Arf-/- mice, elevated KRas signaling is sufficient for tumor formation and does not require activation of Akt signaling. RCAS-KRas-induced tumors arising from both tv-a mouse lines, as described above, are generally sarcoma-like, nestin positive, and Gfap negative. However, the addition of Akt activation seems to influence tumor cells toward an astrocytic character, regardless of cell-of-origin, as is suggested by the overlapping expression of Gfap and HA (a strong indication of elevated Akt activity) in these tumors. In Ntv-a Ink4a-Arf-/- mice, the addition of activated Akt appears to drive the tumor cells toward an astrocytic phenotype (Fig. 3
, compare B and C). On the other hand, in tumors induced by the combination of RCAS-KRas and RCAS-Akt in Gtv-a Ink4a-Arf-/- mice, Akt activation seems to maintain the astrocytic character of the tumor cells, as determined by their continuous expression of Gfap (Fig. 2
, compare C and D). In additional support of this notion, both tumors with GBM-like histology induced by RCAS-KRas alone in Gtv-a Ink4a-Arf-/- mice had elevated levels of endogenous phosphorylated Akt (Fig. 4D
and data not shown), which could not be detected in Gtv-a Ink4a-Arf-/-; KRas induced tumors with spindled morphology.
In KRas + Akt-induced tumors in Ink4a-Arf-/- mice, the addition of Akt activity tended to be phenotypically dominant to Ink4a-Arf loss. As described above, these tumors often displayed a mixed morphology with a gliomatous and a sarcomatous component (Figs. 2A
and 3A)
. Because no gliomas can be induced with Akt alone, all cells in these tumors have to, at some point during tumorigenesis, express activated KRas. Thus, regions that are HA negative can be considered as Kras+/Ink4a-Arf-/- and regions that are HA positive as Akt+/Kras+/Ink4a-Arf-/-. We found a high degree of overlap between HA and Gfap expression (Fig. 2, C and D
and Fig. 3, B and D
) pointing to a phenotypical dominance of Akt activity over Ink4a-Arf loss. In several of the tumors induced in Ntv-a Ink4a-Arf-/- mice, there also seemed to be a morphological dominance of Akt. A number of these tumors displayed regions of spindled cells with sarcomatous morphology not staining for HA in contrast to HA-positive areas within the same tumor that had the characteristic GBM histology (Fig. 3C)
. However, some tumors induced in Ntv-a Ink4a-Arf-/- mice and most induced in Gtv-a Ink4a-Arf-/- mice did not show the distinct morphological dominance of Akt as these tumors had regions comprised of Gfap and HA positive yet spindled cells (Fig. 2, C and D)
.
Ink4a-Arf Loss and Akt Signaling Appears to be Functionally Distinct.
The above data implies that KRas activation can cooperate with either Ink4a-Arf loss or Akt signaling to form gliomas in Ntv-a mice. Although the two tumor types are phenotypically distinct from one another, one possible interpretation of these data could be that Akt signaling and loss of Ink4a-Arf gene expression are functionally linked such that one leads to the other.
To determine whether Akt signaling leads to a phenotype similar to Ink4a-Arf loss in vitro, we compared RCAS-infected primary astrocytes derived from Gtv-a wt and Gtv-a Ink4a-Arf-/- mice for cell proliferation characteristics. Successful infection by RCAS-Akt could be determined with Western blot for HA expression on cell lysates derived from infected cells at day 1 of the proliferation experiment (Fig. 5A)
. In agreement with previous data (22)
, RCAS-lacZ-infected Ink4a-Arf-/- astrocytes grew rapidly (Fig. 5B)
and showed a progenitor phenotype (data not shown). In contrast, RCAS-Akt-infected wt astrocytes grew no more rapidly than RCAS-lacZ-infected wt controls (Fig. 5B)
and showed a flattened morphology (data not shown). Neither did the double infection of RCAS-KRas and RCAS-Akt have a synergistic effect on proliferation in comparison to RCAS-KRas alone. These data indicate that Akt signaling does not convert cells to a phenotype similar to that seen with Ink4a-Arf loss either in vitro or in vivo and implies that the oncogenic effect caused by Akt activation is not caused by stimulating proliferation. Therefore, the two pathways appear functionally distinct, although it cannot be ruled out that they are potentially partly overlapping.
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DISCUSSION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Here we show that experimental Ink4a-Arf loss can efficiently cooperate with KRas activation alone to form CNS tumors from both neural progenitors and differentiated astrocytes in our model system. Because all KRas-induced tumors expressed the neural progenitor marker nestin, even if induced from differentiated astrocytes that normally do not express nestin, this suggests that one role of Ink4a-Arf loss in astrocytes during gliomagenesis is to sensitize these cells to transformation by causing them to dedifferentiate in response to the oncogenic stimuli caused by KRas activation. In additional support of this view, a recent study showed that Ink4a-Arf-deficient astrocytes in vitro acquired a dedifferentiated character in response to the transforming effect of an activated form of the epidermal growth factor receptor (35) .
There are some characteristics of the RCAS/tv-a system that need to be considered when interpreting data derived from it. The first issue regards the relative temporal expression of the tv-a gene product between the two different tv-a transgenic mouse lines. The Ntv-a transgene is driven from the nestin promoter, which is active in several undifferentiated CNS progenitor cell types (31) , whereas the Gtv-a transgene is driven from the GFAP promoter, which is predominantly active in astrocytes (36, 37, 38) . During CNS development, these genes do not appear to have an overlapping expression pattern, and nestin mRNA expression is rapidly decreased in postmitotic cells (33) . The second issue considers the fact that the stability of the tv-a gene product relative to either GFAP or nestin protein in cells during development is unknown. However, with these notions in mind, tv-a-expressing cells in the Ntv-a mice are generally less differentiated than those in the Gtv-a mice, and the advantage of the ability to compare the differentiation status of the cell-of-origin in vivo makes the RCAS/tv-a model valuable for studies such as these.
Because KRas is inefficient to induce tumors in Ntv-a wt mice (0 of 27) and the same applies for the combination of KRas and Akt in Gtv-a wt mice (0 of 68), it seems that spontaneous mutations of the p53 and Rb pathways are rare in our model system. Furthermore, it appears as if the oncogenic collaboration between KRas and Akt is functionally distinct from that of KRas and Ink4a-Arf loss because the resulting tumors have different histological and immunohistochemical properties. Ink4a-Arf loss cooperates with KRas to form sarcoma-like tumors from both nestin-expressing progenitors and astrocytes at equal rates. The presence of activated Akt (endogenous or retroviral) in either cell type, however, directs the tumor cells toward an astrocytic phenotype as determined by the presence of Gfap expression, and this seems to be phenotypically dominant over the effect of Ink4a-Arf loss.
We do not know the mechanism of how activated Akt contributes to the oncogenic process in these tumors. There are numerous downstream effectors of AKT, and it has been ascribed a wide variety of functions, of which, some of the more likely applied to our model will be briefly discussed. AKT may enhance cell survival by protecting tumor cells from apoptosis (39) . Several reports suggest that AKT is involved in G1 cell cycle regulation. One study proposed that activation of Akt by HER-2/neu can facilitate phosphorylation of p21CIP1 that would cause a cytoplasmic localization of p21CIP1 protein (40) . HER-2/neu activation of AKT has also been shown to lead to p53 degradation via phosphorylation of MDM2 (41) . However, a recent study proposed that the AKT-induced phosphorylation of p21CIP1 caused stabilization of the p21CIP1 protein and inhibition of PCNA binding, possibly promoting cell survival and chemoresistance of tumor cells (42) . There are also reports suggesting that deregulated Akt may be involved in aberrant cell growth. In neurons lacking Pten in vivo, high levels of phosphorylated Akt could be found, and cells showed an increase in soma size (43 , 44) . Interestingly, all multinucleated giant cells investigated in our tumors were strongly positive for HA.
As mentioned above, the histology of KRas-induced tumors in Gtv-a Ink4a-Arf-/- and Ntv-a Ink4a-Arf-/- mice was spindled sarcoma-like lesions, similar to human primary brain sarcomas. The majority of these tumors were Gfap negative. However, a few of the tumors derived from Gtv-a Ink4a-Arf-/- mice had regions still expressing Gfap. The addition of Akt activation created tumors with a mixed histology of sarcoma and GBM. In the Ntv-a Ink4a-Arf-/- background, the sarcomatous parts were mostly Gfap negative, but if derived from Gtv-a Ink4a-Arf-/- mice, spindled cells could be either positive or negative. Some of these tumors also had rather extensive areas of giant, multinucleated cells. The resulting tumor types caused by these combinations histologically closely resembled human GBM and several different rare subtypes thereof such as spindle cell GBM, GS, and giant cell GBM, for which there have been no genetic animal models described previously.
Human GS tumors are composed of two distinct tumor histologies, spindle cell sarcoma, which is GFAP negative, and GBM, which is GFAP positive. It is not known whether the two tumor types arise from two independent cells or have a common origin. Some studies suggest that the sarcomatous portion could have mesenchymal origin, possibly being derived from microvascular proliferations within a GBM (45 , 46) . However, other reports based on genetic data strongly indicate that the two components could indeed be derived from one common cell that evolves into two distinct morphological subgroups (47 , 48) . Our tumors derived from either the Ntv-a Ink4a-Arf-/- or the Gtv-a Ink4a-Arf-/- mice clearly support the view that the sarcomatous part of a GS can be derived from neural progenitors and astrocytes. In view of the data presented in this report, it seems plausible that human primary brain sarcoma, GS, spindle cell GBM, giant cell GBM, and standard GBM may be closely related tumors existing in a spectrum of cell-of-origin and variable activities of signal transduction and cell cycle arrest pathways.
Is INK4a-ARF loss required for GBM formation? The answer appears to be yes in some cases and no in others. In progenitor cells and astrocytes with elevated KRas signaling, Ink4a-Arf loss allows glioma formation. However, in progenitor cells, elevated Akt signaling appears capable of substituting for the oncogenic contribution of Ink4a-Arf loss. In human GBMs, both elevated AKT activity and INK4a-ARF loss are frequently found, and the histology of these tumors varies regionally, hence the name GBM multiforme. This, in combination with our data, implies that the cell-of-origin for these tumors could in some cases be differentiated astrocytes. In addition, regional variability in the activity of specific signal transduction pathways may exist within a GBM and explain the frequent occurrence of both elevated AKT signaling and INK4a-ARF loss. Such regional variability in oncogenic combinations may give rise to the observed multiforme nature of GBM and imply that failure to therapeutically address all oncogenic combinations simultaneously may be a lethal oversight.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 L. U. is supported by a postdoctoral grant from the Swedish Cancer Society, and E. C. H. is supported by NIH Grant RO1 CA94842, the Searles Scholars Program, and the Tow Foundation. 
2 To whom requests for reprints should be addressed, at Department of Cell Biology, Memorial Sloan-Kettering Cancer Center, RRL 961, 1275 York Avenue, New York, NY 10021.
3 The abbreviations used are: GBM, glioblastoma; CNS, central nervous system; RTK, receptor tyrosine kinase; PI3k, phosphoinositide 3'-kinase; RB, retinoblastoma; Gfap, glial fibrillary acidic protein; wt, wild type; RCAS, Replication Competent ALV Splice; HA, hemagglutinin; GS, gliosarcoma; ALV, avian leukemia virus; RCAS, replication competent ALV splice acceptor.
Received 4/ 1/02. Accepted 7/31/02.
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REFERENCES |
|---|
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. Cell, 103: 931-943, 2000.[Medline]
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|
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|
|
|
|
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|
|
|
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 |
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|
|
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|
|
|
|
|
|
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|
|
|
|
|
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|
|
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|
|
 |
|
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|
|
|
|
 |
|
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|
|
|
|
|
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L. Uhrbom, M. Kastemar, F. K. Johansson, B. Westermark, and E. C. Holland Cell Type-Specific Tumor Suppression by Ink4a and Arf in Kras-Induced Mouse Gliomagenesis Cancer Res., March 15, 2005; 65(6): 2065 - 2069. [Abstract] [Full Text] [PDF]
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A. T. Kho, Q. Zhao, Z. Cai, A. J. Butte, J. Y.H. Kim, S. L. Pomeroy, D. H. Rowitch, and I. S. Kohane Conserved mechanisms across development and tumorigenesis revealed by a mouse development perspective of human cancers Genes & Dev., March 15, 2004; 18(6): 629 - 640. [Abstract] [Full Text] [PDF]
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Z.-y. Huang, Y. Wu, S. P. Burke, and D. H. Gutmann The 43,000 Growth-associated Protein Functions as a Negative Growth Regulator in Glioma Cancer Res., June 1, 2003; 63(11): 2933 - 2939. [Abstract] [Full Text] [PDF]
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) and spindle cell (arrows) regions positive for nestin (B), Gfap (C), and HA (D); scale bar = 50 µm. E–H show a giant cell GBM-like tumor. H&E staining of giant cells (E) and immunohistochemical analysis for expression of nestin (F), Gfap (G), and HA (H); scale bar = 100 µm.
